I read somewhere that being young (less than 18) and female increases my risk of a re-tear of an ACL repair (which I had done about six months ago). Can you tell me why these two things are the reason for another injury? I am both female and turning 18 this year and I definitely don’t want to go through this again!

Most people who have surgery to reconstruct a ruptured anterior cruciate ligament (ACL) expect that procedure to be the only one they have done on the knee. But unfortunately, there is a group of patients who end up needing a second knee surgery — and even sometimes surgery on the other leg. How can you tell if this scenario might happen to you?

An investigation performed at the Vanderbilt University Medical Center in Nashville, Tennessee may shed some light on both the rate of second surgeries and the risk factors (or “predictors”) for subsequent surgeries. With as many as 200,000 ACL surgeries done each year in the United States, surgeons and patients alike may benefit from the information this study provided.

They followed almost 1,000 patients over a period of six years after ACL reconstructive surgery on one leg. They found a surprising number of patients required additional knee surgery on the same leg that had the first ACL reconstruction (18.9 per cent). That is almost one out of every five patients. And another 10 per cent (one out of every 10 patients) later had surgery on the other knee.

What happened that these patients required further procedures and why? Analysis of the data revealed what you have heard: that younger patients (younger than 18 years) were more likely to need further surgery. Younger patients with a ruptured ACL may just be more active putting them at increased risk of further problems. Or they may not follow the physician’s and physical therapist’s instructions after surgery. This type of noncompliance could be a factor but was not determined in this study.

One other patient-related factor was mentioned but not studied: the potential for reinjury based on genetic features such as collagen disruption affecting both ligaments and cartilage. A third risk factor (predictor) was the use of an allograft (from a donor rather than from the patient) to reconstruct the damaged ACL. This factor falls under the category of surgical technique (rather than being a patient-related factor).

The authors questioned whether being overweight or female might be other risk factors or predictors of subsequent knee surgeries. But this was not the case in this study. Other studies have reported higher reoperation rates among females. In general, the overall evidence does not show a difference in male versus female reoperation rates.